1. Field of the Invention
The present invention relates generally to a dust cover adapted to cover a piston rod etc. of a shock absorber which constitutes an automotive suspension mechanism and to prevent adhesion of grit, water or the like, for example.
2. Description of the Related Art
Conventionally, there is known a dust cover which prevents adhesion of grit, water or other foreign matters, and for example, by being externally fitted around a shock absorber and covering the periphery of the projecting part of a piston rod, the dust cover is used for preventing adhesion of the foreign matters to the piston rod or the like. The dust cover overall has a thin-walled tubular shape formed of a rubber elastic body, synthetic resin or the like, and is capable of extension/contraction in the axial direction according to the projecting amount of the piston rod from the cylinder by including a bellows tube portion having a plurality of main valleys of concave shape opening towards the outer periphery of the tube portion and arranged in a linked manner. Such a dust cover is disclosed in U.S. Pat. No. 8,657,270, for example.
Meanwhile, it is desirable that the axial minimum dimension of the dust cover during contraction be small so as to follow a large contraction of the shock absorber due to input from the road face. In order to make the minimum dimension of the dust cover small, it is conceivable to reduce the number of the main valleys that constitute the bellows tube portion so that the length during contraction is set small. Besides, the dust cover is required to have an initial length that is able to duly cover the entire projecting part of the piston rod in an installed state. Thus, in order to reduce the number of the main valleys while obtaining a sufficient length of the bellows tube portion, it is necessary to enlarge the slope angle of the slope wall portion of each main valley so as to ensure a large axial width of each main valley.
However, if the slope angle of the slope wall portion of the main valleys is enlarged, when the bellows tube portion is subjected to the axial force and undergoes contraction, compressive component applied to the slope wall portion is larger relative to shear component. Accordingly, the slope wall portion is likely to buckle, posing a risk of inhibiting smooth contraction of the bellows tube portion.